This may be true that they are lazy in developing a blesta module. However, the plugin benefits Blesta more than Namesilo. I don't foresee any Namesilo members choosing Blesta over Namesilo. In the end, Namesilo members will be forced to other hosting applications.
Remember, people don't buy hosting applications and then see which domain registrars are available. It works the other way around. Those who are members of domain registrars look to see which hosting platform is available for them. Therefore, Blesta's growth depends on which providers are supported, but domain registrars aren't dependent on which hosting platform supports them. People get domains first.
Not too long ago a Clientexec plugin popped up on Namesilo. So that will leave Blesta out of the mix. I have a Hostbill and WHMCS license. However, development is more open on Blesta (for which I have use for custom plugins I want developed). However, if I cannot , why would I consider Blesta over the others?
I do hope a Namesilo plugin is developed though. I'd like to invest in Blesta because of it's openess in which I can have customization. Because of this, I would invest in Blesta for a long term.
My suggestion would be: If it's sooo simple to develop a Namesilo plugin, Blesta should just lose the ego and take the small amount of time to get it done, an done well to start capturing more sales, which would help in further development and growth. A simple business logic, from a Business Analyst.
Just food for thought.